What does 'Udûn' mean in 'The Lord of the Rings: The Rings of Power'?

The word "Udûn" plays a large role in episode 6 of The Lord of the Rings: The Rings of Power. For one thing, it's the title of the episode. For another, it's the victory chant taken up by the orcs as Adar's (Joseph Mawle) plan for the Southlands finally falls into place.

As episode 6 reveals, Adar didn't simply want the hilt...